Automatic velocity component selector for electronystagmographs

ABSTRACT

An improved apparatus for recording the velocity components in electronystagmographs. The eye position signals obtained from sensors attached to a patient undergoing nystagmus tests are coupled to a differentiator. The output of the differentiator is attached, through switch means, to a pen actuated recorder to provide an analog recording of the velocity derivative under desired test conditions. Means are provided to readily set the pen to zero at a mid-graph location, at a top-graph location and at a bottom-graph location thereby enabling the positive and negative velocity components to be shown on the entire graph scale.

nite States Patent [191 Servos Feb. 26, 1974- AUTOMATIC VELOCITYCOMPONENT SELECTOR FOR ELECTRONYSTAGMOGRAPHS 21 Appl. No.: 104,936

[52] US. Cl 128/2.1 R [51] int. Cl A611) 5/05 [58] Field of Search.....128/2 N, 2 S, 2 T, 2 R, 2 Z, 128/2.1 R, 2.1 B

[56] References Cited UNITED STATES PATENTS 3,563,231 2/1971 Ducote eta1. l28/2.l R 3,123,768 3/1964 Burch et al... l28/2.1 B 3,217,70611/1965 Sullivan 128/2.1 R 3,000,271 9/1961 Harvey et a] l28/2.l R

3,258,008 6/1966 Durand l28/2.l R 2,902,030 9/1959 Kennedy et al.128/2.l R

McGrawHill 1956, 2nd Ed. Copy in Scientific Library (QA 76.4 1(6), pp.13 & 415.

Primary Examiner-Kyle L. Howell Q Attorney, Agent, or FirmAlter WeissWhitesel & Laff [5 7] ABSTRACT An improved apparatus for recording thevelocity components in electronystagmographs. The eye position signalsobtained from sensors attached to a patient undergoing nystagmus testsare coupled to a differentiator. The output of the differentiator isattached, through switch means, to a pen actuated recorder to provide ananalog recording of the velocity derivative under desired testconditions. Means are provided to readily set the pen to zero at amid-graph location, at a top-graph location and at a bottomgraphlocation thereby enabling the positive and negative velocity componentsto be shown on the entire graph scale.

7 Claims, 3 Drawing Figures AUTOMATIC VELOCITY COMPONENT SELECTOR FORELECTRONYSTAGMOGHS This invention relates to apparatus used formeasuring nystagmus responses in the human body and more particularly toapparatus for automatically recording the velocity component ofnystagmus movement.

It is now recognized in the diagnostic medicinal field that thephenomena known as nystagrnus can be used to ascertain vestibulardisorders. There is apparatus presently available which records therelative position of a patients eyeballs under conditions of induced orspontaneous nystagmus.

Nystagmus may be induced by many known methods. This invention is notconcerned with the method of inducing the nystagmus; but, is concernedwith the apparatus utilized in recordingthe velocity of the movement ofthe eyeball and is especially concerned with apparatus for recording theslow components of the velocity of the movement of the eyeball. Moreparticularly, it has been found that under conditions of nystagmus, theeyeball will move relatively slowly to the right or to the left and thenmove at a much higher velocity towards the starting eyeball position.That is, the eyeball oscillates under induced nystagmusconditions,.moving to the right or left side of the eye cavity in thecranium. When the eyeball reaches the limit of such movement, it movesback towards the starting position at a relatively high rate of speed.

The known methods of measuring the eyeball velocity record the positionof the eyeball on graph paper against a time base. Technicians thencompute the slope of the trace on the graph paper to determine the timedifferential of the position; which is of course the velocity. Thetechnician performing the test has to determine the velocity of theeyeball under nystagmus conditions when the eyeball is moving to theright and when the eyeball is moving to the left. Thus, in the known andused velocity computing procedure, there is a wide latitude for errorbecause of the relatively larger number of individually performed steps.

Accordingly, an object of this invention is to provide direct velocityreadings derived from the analog position signals denoting the positionof the eyeballs and to ascertain whether the analog signals are causedby stimulating the left tympanic membrane with a colder condition, theright tympanic membrane with a colder condition, the left tympanicmembrane with a warmer condition, and the right tympanic membrane with awarmer condition.

A related object of the present invention is to provide for full scalereading when the pen movement is to the left and a full scale readingwhen the pen movement is to the right. This requires changing the zeroposition of the pen from a mid-graph location to a top or bottom graphlocation.

Yet another object of the invention is to automatically differentiatethe positional signal to obtain the velocity signal.

Still another object of the invention is to differentiate the positionalsignal and read only the positive output of the differentiator.

A related object of the invention is to automatically select thetympanic membrane bath temperature.

Yet another related object of the invention is to zero the pen at thebottom of the scale when only the positive signals are read and to zerothe pen at the top of the scale for a zero location when only thenegative signals are read.

The above mentioned and other objects and features of this inventionwill become more apparent from a description of the apparatus in thefollowing specification taken in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a block diagram showing of the apparatus utilized for takingpositional readings of the eyeballs along a horizontal axis underconditions of induced nystagmus;

FIG. 2 is a schematic showing of apparatus utilized to record thevelocity outputs obtained by differentiating the positional signalsobtained by the apparatus of FIG. 1; and

FIG. 3 is a graphic showing of the position and velocity componentsobtained from the equipment of FIG. 1 and FIG. 2, respectively.

Turning now to the drawings, FIG. 1 shows in block diagram formapparatus, generally designated as 10 for recording the position of theeyeball under nystagmus. More particularly, means are provided forsensing the cornea-retina potential difference at the patients temples.For example, electrodes 11 and 12 are fastened by means, such asadhesive tape, to the patient. The pa tient is shown in dotted lines inFIG. 1. In applying the electrodes, the skin surface of the patient isfirst cleaned with a solvent, such as alcohol, or the like, to degreasethe skin. An electrically conducting jelly is then applied to the areasof placement of the sensors to reduce the contact resistance to minimalvalues. The electrodes are then fastened to the patients head.

This example is given showing electrodes 11 and 12 for detecting thecornea-retina potentials difference.

Electrodes can also be fastened above and below each eye to measure thevertical movements of the eyeballs. The operation of the invention wouldbe as effective under such conditions as they are for the horizontalmeasurements described in detail hereinafter.

The output signal of each of the electrodes 11 and 12 are coupled to ahigh gain amplifier 13 through leads 14 and 16, respectively' Theamplified output of the high gain amplifier is coupled to drive arecording oscillograph. Responsive to the receipt of the amplifiedsignal from amplifier 13, the pen 18 of the oscillograph 17 is drivenfrom its central zero location either upwardly or downwardly to providea trace showing the position of the eyeball. When the eyeball ispositioned so that the patient is looking directly forward, the penshould be in a zero location. Any movement of the eyes to the right orto the left produces a cornea-retinal potential that is a function ofthe distance the eyes have moved from the zero location.

The nystagmus-condition is stimulated by causing a temperaturedifferential between the tympanic membranes of the right and left ears.The temperature differential or caloric stimulation condition isobtained in many Ways. One preferred method is to flood a selected earcanal with water at a desired temperature to stimulate the tympanicmembrane of that ear. Each ear is stimulated with water at atemperature, either 7 C above or 7 C below the normal body temperature.The water that is at a temperature which is 7 C above the normal bodytemperature is called the hot temperature, and the water which is at atemperature 7 C below the normal body temperature is called the coldtemperature.

The apparatus provided and described hereinafter records the elicitednystagmus automatically including the slow velocity component; i.e., thevelocity of the eyeball in its travel from the original forward viewingpoint to the point at the edge of the eye socket.

Means are provided for stimulating the tympanic membrane. Moreparticularly, water at the desired temperature is flushed into theselected car through tube 19, subjecting the tympanic membrane to adifferential temperature, and thereby causing nystagmus wherein the eyeoscillates.

In the past, to obtain the velocity component, the trace recorded by theapparatus of FIG. 1 was analyzed to determine the slope of each portionof the trace. Since the recording has a time base on the abscissa, theslope of the curve or trace at any point is the time differential of theposition or the velocity of the eyeball.

Means are provided for utilizing the output of amplifier 13 toautomatically differentiate the signal obtained from the amplifier 13.More particularly, lead 21 is coupled directly to the lead 22 thatconnects amplifier 13 to recorder 17. A switch 23 may be provided toconnect point A to the output of amplifier 13.

Means are provided for differentiating the signal from amplifier 13.More particularly, point A is coupled to a differentiating circuit,shown generally as circuit 24 in FIG. 2. The coupling occurs through aseries capacitance resistance coupling network, wherein capacitor C1 isin series with resistor R1 at the input of operational amplifier 26. Theoperational amplifier is converted to a differentiator by utilizing thebridged RC feedback network, comprising a bridged capacitor C2 andparallel resistor R2 connecting the input and the output of operationalamplifier 26.

Means are provided for connecting the differentiated output of amplifier26 to the recorder. More particularly, switch means 27 comprising adiode network, generally shown as 28, and a multi-level rotary switchgenerally shown as 29 are used to couple the differentiated output tothe oscillograph recorder 31. The oscillograph recorder 31 can berecorder 17 switched over to receive the output from switch means 29.The switch means 29 comprises a plurality of simultaneously operatedrotors, such as rotors 32, 33, and 34. The switch has an off position, aleft cold position, a right cold position, a left hot position, a righthot position and a both position. Rotor 32 is the rotor which couplesthe differentiated signal into the power amplifier 35. Rotor 33 is therotor which couples a bias voltage into a power amplifier 35 inoscillograph recorder 31 to cause the pen motor 36 to move the pen 37 toa zero location on the chart paper. Rotor 34 actuates a water bathtemperature selector relay to automatically select the desiredtemperature of the water used.

The output of operational amplifier 26 is coupled directly to the bothposition of stator 38. When the tympanic membrane of the left ear of thepatient is stimulated by the cold water, only negative signals areelicited from the differentiator during the time the eye travels towardthe end of the socket. Note that the velocity in that direction is theslow component. Similarly, when the tympanic membrane of the right earof the patient is stimulated with hot water, only negative signals areforthcoming from the operational amplifier, while the eye is travelingtoward the end of the socket. In other words, the slow component of thevelocity is measured.

To assure that only the negative signals are picked up during the periodof the test wherein the left ear is supplied with cold water, or theright ear is supplied with hot water, the stator positions of the switchRH and LC are tied together and coupled through negative going diode D1to the output of the operational amplifier 26. A biasing resistor R3connected from the common point of stator position RH and LC to groundis provided. Thus, only negative signals are coupled to the oscillographrecorder when switch rotor 32 is connected to positions LC and RH ofstator 38.

In a similar manner, when the right ear is stimulated with cold water,and the left ear is stimulated with hot water, the positive signalsemitted by the operational amplifier 26 represents the slow component ofthe velocity of the eye during nystagmus. The eye moving in thedirection toward the end of the eyeball cavity generates a positivesignal of the sensors. A positive going diode D2 is thus connected tothe point common to switch positions RC and LH on stator 38. A biasingresistor R4 is provided at this common point.

Wipers 32, 33 and 34 move simultaneously. Thus, when wiper 33 moves tostator position LC on stator 39, then the power amplifier 35 of therecorder 31 is positively biased to drive the pen 37 toward the top ofthe graph paper. In one preferred embodiment, the pen is zeroed withinfive millimeters of the top edge of the graph paper. Thus, any negativesignals received through wiper 32 can utilize the entire scale of therecorder. Similarly, when wiper 33 is connected to position RC or LH onstator 39, then the power amplifier 35 is biased negatively to drive thepen 37 within five millimeters of the bottom of the paper; thereby,providing a complete full scale reading for the positive signalsreceived through the diode D2.

It should be noted that the positive voltages are coupled to the commonstator position, RH and LC of stator 39 through a variable resistor R6,which can be varied by moving the associated wiper up and down forvernier control of the zero pen position by any well known means, suchas the screw driver adjustment 41. Similarly, the negative bias voltagecan be varied utilizing variable resistor R7 through means such as screwdriver adjustment 42.

FIG. 3 shows an idealized form of the curves of the recorder 17 at A andof the recorder 31 at B. The abscissas of both graphs is the time axissince the recorder paper is moved synchronously from its roll. Thenystagmus conditions results in the movement of the eyeball which isrecorded positionally on recorder 17, as shown in Graphs Al and A2.Therein, the position of the eye is shown as it moves from the startposition, shown as X or V, respectively, to one end of the eye socket,shown as Y or W, respectively. After reaching the end, the eye returnsto its start position. This is shown as points X, V, respectively. Theeye continues to move to the other end of the socket, shown as positionY. Then, it returns to the start point X.

The velocity component of this movement is shown by the curve traced onrecorder 31 and is idealized in curves B1, B2. Therein, the lineportions XY and VW, respectively represent a first velocity that isequal to the slope of line portions XY and VW, respectively of curvesA1, A2, respectively. The line portion XY is a relatively slow velocitycomponent. The slope of curve A1 then reverses to a positive sloperepresented by line portion YY of curve A1; which is the relatively fastvelocity component. At point Y of curve All, the slope once againchanges to a negative slope equal in value to the line segment orportion Y'X of curve All. The slope of line portion Y'X is smaller thanthe slope of the previous portion of the line positions YY'. Curve Althus represents the left slow and fast velocity component. Similarly,the line portions VW WV represents slow velocity components and arepositive while line portion W'W' represents a negative fast velocitycomponent.

The curves shown in FIG. 3B are the curves when both positive andnegative signals are coupled from the differentiator 24 to recorder 31.The portion of curves Bl, B2 labeled XY, Y'X and W'W' are the portionsof the curve that would be shown when only the negative signals areallowed through diode D1; that is, when wiper 32 is either on positionRC or position LC of stator 38. In that case, the offset control ofstator 39 would be used to adjust the positive biasing voltage to drivethe pen up to within 5 millimeters of the top of the scale at its zeroposition. Thus, the entire width of the paper is then used todemonstrate the exact velocities being recorded. Similarly, when theportions YY, VW and W'\/ are being recorded; i.e., when the wiper 32 isconnected to position RC and LH of stator 3%, then diode D2 allows onlythe positive signals through. At that time, the offset control 42 isoperated and the negative biasing is connected to the power amplifier 34in the oscillograph to drive the pen to within five millimeters of thebottom of the scale at its zero position. A full scale reading of thevelocity represented by the line portions YY', VW and WV are thusobtained.

In operation, the patient sits in a chair with the sensors attached, aspreviously described. The potential generated in the movement of thepatients eyes is first checked out by directing the patient to lookfirst at an originating spot or light, and-subsequently to spots orlights on either side of the first originating spot (or light), therebycausing the patients eyes to move a calibrated distance. This providesan absolute indication of the voltages through the system during themovement of the eye. This calibration may also be accomplished after thetesting; then switch 29 is placed in the off position.

Initially, the switch is set to the B position. Neither tympanicmembrane is stimulated; instead, the patient is told to close his eyesand his head is moved to several attitudes. Recordings are also made.This measurement acts to determine spontaneous nystagmus.

Now caloric tests are made. The head is placed on a 30 angle and thepatient sits in the chair and cold water, 7 C below his bodytemperature, is applied through the tube 19 to his left ear. Thevelocity recorder is connected into the system through switch 23. Byoperating switch means 27 so that wipers 32, 33 and 35 are on positionLC, and inundating the left ear a direct velocity reading is obtainedcorresponding to portion XY on curve B of FIG. 3, except that the pen 37is centered at the top of the graph paper.

When the cold water supply is used to flood the right ear, the velocityis again measured. The new portion VW of B2 is read directly onoscillograph 31 with pen 37 zeroed juxtaposed to the bottom of the graphpaper.

The left ear is then supplied with hot water. The switch means isswitched to the LH position. Once again, the velocity is read directly.This time it is represented by portion VW of curve B2 of FIG. 3. The penis zeroed at the bottom of the page. Then, the hot water is supplied tothe right ear to stimulate the right tympanic membrane and once againelicit nystagmus condition in the patient. This time, the switch is inthe RH position, and the pen is positioned at the top of the page.

Thus, it is seen that the system provides a unique and foolproofapparatus which can be reliably operated by ordinary technicians. Itdoes not require any special training or skill to operate the equipment.

While the principles of the invention have been described above inconnection with specific apparatus and applications, it is to beunderstood that this description is made only by way of example and notas a limitation on the scope of the invention.

I claim:

1. An improved apparatus for automatically measuring the eyeballvelocity characteristics of a patient under conditions of nystagmus byapplying distinct hot and cold temperature differentials to the tympanicmembranes of the patient for diagnosing vestibular disorders,

said apparatus comprising selecting means for induc ing mystagmus in apatient by applying distinct ones of said hot and cold temperaturedifferentials in a sequential manner,

means for sensing the cornea-retina voltages indicative of the movementof the patients eyes across the eye sockets,

amplifying means for amplifying said voltages,

velocity converting means for automatically convertingvsaid voltages tovelocity indications, said velocity converting means comprisingdifferentiating means for differentiating said voltages, and

said selecting means also simultaneously coupling,

the output of said differentiating means to indicating means,

said selecting means further comprising means for coupling only the slowvelocity components of each of said velocity indications to saidindicating means under the distinct ones of said hot or colddifferentials.

2. The improved apparatus of claim 1 wherein differentiating meanscomprises operational amplifier means,

parallel resistor-capacitor network means for interconnecting the inputand the output of said operational amplifier, and

series resistor-capacitor network means for coupling said voltages tothe input of said operational amplifier.

3. The improved apparatus of claim 1 wherein said indicating meanscomprises recording means,

said recording means comprising a movable media for recordingindications thereon,

pen means for making indications on said media,

motor means for moving said pen means transverse to the movement of saidmedia as a function of the output of said differentiating means, and

said selecting means comprising switching means for coupling the outputof said differentiating means of said motor means at each of saidvariety of conditions.

4. The apparatus of claim 3 wherein said means for coupling only saidslow velocity component to said pen motor means comprises diode meanscoupled between said first diode coupled between the output of said 10differentiator and the right cold and left hot positions of said switchwhen the left tympanic membrane of the patient is exposed to the hottemperature and the right tympanic membrane of the patient is exposed tothe cold temperature. 6. The apparatus of claim 5 wherein said means forcoupling only the slow velocity component to said pen motor meanscomprises a second diode positioned to pass negative signals and blockpositive signals,

said second diode coupled between the output of said differentiator andthe switching positions of said switch when the left tympanic membraneof the patient is exposed to the cold temperature and when the righttympanic membrane of the patient is exposed to the hot temperature.

7. The improved apparatus of claim 6 wherein means are provided fornormally positioning said pen motor approximately at the mid point ofsaid media when the velocity is zero, and

means for positioningsaid pen at the opposite extremes of said mediawhen the output of said differentiating means is coupled to saidrecorder means through said positive and negative going diode, re-

spectively.

UE*? '.EED STAKES PNH'LNT OEI'FICE @A'II: 0F {ZQRRLCTIQN Patent No. 3, 017 V Dated I February 26, 1974 Inventor(s5 Gerald H. Servos It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

N THE SPECIFICATION C01. 6, line 24; after "ing" change -"mystagmims" to--nystagmu s-.

Signed end s eal'edvt his 13th day of August 197 (SEAL) Attest:

MCCOY M. GIBSONQ'JR. c. MARSHALL'DANN Attesting Officer Commissioner ofPatents

1. An improved apparatus for automatically measuring the eyeballvelocity characteristics of a patient under conditions of nystagmus byapplying distinct hot And cold temperature differentials to the tympanicmembranes of the patient for diagnosing vestibular disorders, saidapparatus comprising selecting means for inducing mystagmus in a patientby applying distinct ones of said hot and cold temperature differentialsin a sequential manner, means for sensing the cornea-retina voltagesindicative of the movement of the patient''s eyes across the eyesockets, amplifying means for amplifying said voltages, velocityconverting means for automatically converting said voltages to velocityindications, said velocity converting means comprising differentiatingmeans for differentiating said voltages, and said selecting means alsosimultaneously coupling, the output of said differentiating means toindicating means, said selecting means further comprising means forcoupling only the slow velocity components of each of said velocityindications to said indicating means under the distinct ones of said hotor cold differentials.
 2. The improved apparatus of claim 1 whereindifferentiating means comprises operational amplifier means, parallelresistor-capacitor network means for interconnecting the input and theoutput of said operational amplifier, and series resistor-capacitornetwork means for coupling said voltages to the input of saidoperational amplifier.
 3. The improved apparatus of claim 1 wherein saidindicating means comprises recording means, said recording meanscomprising a movable media for recording indications thereon, pen meansfor making indications on said media, motor means for moving said penmeans transverse to the movement of said media as a function of theoutput of said differentiating means, and said selecting meanscomprising switching means for coupling the output of saiddifferentiating means of said motor means at each of said variety ofconditions.
 4. The apparatus of claim 3 wherein said means for couplingonly said slow velocity component to said pen motor means comprisesdiode means coupled between said selecting means and the output of saiddifferentiator.
 5. The apparatus of claim 4 wherein said diode meanscomprises a first diode to pass positive signals and block negativesignals, said selecting means having switching positions including leftcold, right cold, left hot, right hot and both positions in accordancewith the said variety of conditions, said first diode coupled betweenthe output of said differentiator and the right cold and left hotpositions of said switch when the left tympanic membrane of the patientis exposed to the hot temperature and the right tympanic membrane of thepatient is exposed to the cold temperature.
 6. The apparatus of claim 5wherein said means for coupling only the slow velocity component to saidpen motor means comprises a second diode positioned to pass negativesignals and block positive signals, said second diode coupled betweenthe output of said differentiator and the switching positions of saidswitch when the left tympanic membrane of the patient is exposed to thecold temperature and when the right tympanic membrane of the patient isexposed to the hot temperature.
 7. The improved apparatus of claim 6wherein means are provided for normally positioning said pen motorapproximately at the mid point of said media when the velocity is zero,and means for positioning said pen at the opposite extremes of saidmedia when the output of said differentiating means is coupled to saidrecorder means through said positive and negative going diode,respectively.